Power over Ethernet (PoE) is a technology that transmits both Ethernet data and power using a twisted pair, where the power refers to supplied electricity.
According to rules of the Telecommunications Industry Association (TIA)/Electronic Industries Alliance (EIA) 568 (TIA/EIA-568), a cable pair 3 includes a cable (cable 1) connected to a pin 1 and a cable (cable 2) connected to a pin 2 that are in an 8 position 8 contact (8P8C) modular connector of an Ethernet twisted pair, and a cable pair 2 includes a cable (cable 3) connected to a pin 3 and a cable (cable 6) connected to a pin 6 that are in the 8P8C modular connector. A cable pair 1 includes a cable (cable 4) connected to a pin 4 and a cable (cable 5) connected to a pin 5 that are in the 8P8C modular connector, and a cable pair 4 includes a cable (cable 7) connected to a pin 7 and a cable (cable 8) connected to a pin 8 that are in the 8P8C modular connector.
A PoE device includes two categories: power sourcing equipment (PSE) and a powered device (PD), and the PoE device may also be both the PSE and the PD. The PSE is equipment supplying power to the PD. The PD is a device, for example, an Internet Protocol (IP) telephone, a web camera, a wireless access point (AP), a personal digital assistant (PDA), an IP camera, a light emitting diode (LED) lamp, or a notebook computer, that receives power.
Conventional PSE supports supplying power using only two cable pairs. For example, the PSE supports supplying power using only a cable 1, a cable 2, a cable 3, and a cable 6 that are in an Ethernet twisted pair, or using only a cable 4, a cable 5, a cable 7, and a cable 8 that are in an Ethernet twisted pair. For example, if the PSE supplies power using the cable 1, the cable 2, the cable 3, and the cable 6 that are in the Ethernet twisted pair, the PSE sends a detection signal to a peer end, and when detecting that a resistance and a capacitance of the peer end fall within a given range, for example, the resistance falls within a range of 19 kilohm (10 to 26.5 kΩ, and the capacitance is 0.150 microfarad (μF), the PSE determines that the peer end is connected to a valid PD.
A negotiation level between the PSE and the PD is level 0 to level 4. When the negotiation level is level 4, the PSE supplies maximum power, and output power is approximately 30 watt (W). With development of PoE application, categories of the PD become increasingly rich, and there are more PDs having a power requirement of being greater than 30 W, and are generally referred to as high power powered devices. When a power required by a PD is greater than 30 W, the PSE needs to supply power using four cable pairs, that is, supply power to the PD using both a first set of cable pairs and a second set of cable pairs. The first set of cable pairs, also referred to as an Alternative A (ALT A), includes a cable pair 2 and a cable pair 3, that is, includes a cable 1, a cable 2, a cable 3, and a cable 6. The second set of cable pairs, also referred to as an Alternative B (ALT B), includes a cable pair 1 and a cable pair 4, that is, includes a cable 4, a cable 5, a cable 7, and a cable 8.
However, currently, when supplying power using four cable pairs, the PSE still cannot distinguish PDs of different design types. Therefore, the PSE cannot supply power to a PD correctly and effectively according to a design type of the PD at a peer end, resulting in cases in which supplied power is insufficient, causing a power outage of the PD, or distributed power is excessively high, causing a waste of system power.